1. Field of the Invention
The present invention relates in general to a cassette tape recorder of automatic reverse type. More particularly, the present invention relates to a shift mechanism for a head base carrying a head and a pair of pinch rollers at opposite sides of the head. The shift mechanism of the present invention allows the base plate to move in an oblique direction so that a selected one of the pinch rollers is pressed against a corresponding capstan while the other pinch roller remains uncontact with its corresponding capstan.
2. Description of the Prior Art
In a typical auto-reverse mechanism of a conventional type, each pinch roller is assembled in a housing which may be moved by a push member slidably mounted on a head base. When the push member is moved in one direction, one of the pinch roller housings is moved to be in press-contact with one of flywheels so that a tape is running in one direction for forward play. When the push member is moved in an opposite direction, another pinch roller housing becomes in press-contact with another flywheel so that the tape is running in an opposite direction for reverse play.
This conventional mechanism requires separate housings and push members for each of the pinch rollers, which increases the number of parts in the cassette tape recorder and, therefore, has a large size with a complex structure. It should be manufactured at a higher cost.
The present inventor proposed a cassette tape drive apparatus in the U.S. Pat. No. 4,935,831 which includes a projection at a leading end of a rotary bar driven by a motor, and a pair of arms engageable with the projection. While one of the arm rotates due to engagement with the leading end of the rotary bar, a head base is moved from its stand-by position toward a tape running plane. This mechanism, however, only allows parallel movement of the head base, and requires another mechanism for movement of a pinch roller.
Accordingly, it is a principal object of the present invention to obviate the above-described disadvantages of the conventional auto-reverse mechanism in a cassette tape recorder.
Another object of the present invention is to provide a head base shift mechanism of a novel and simple construction in an auto-reverse mechanism, which can be manufactured by addition of the minimum number of parts to a one-way drive mechanism.
Still another object of the present invention is to provide a mechanism of a compact design for shifting a head base carrying a head and a pair of pinch rollers at opposite sides of the head, in one of oppositely oblique directions to be selected upon a tape running direction.
In accordance with an aspect of the present invention, there is provided a head base shift mechanism in a cassette tape recorder of automatic reverse type, comprising a motor; a chassis with a pair of capstans rotatable in forward and reverse directions; a head base slidably mounted on the chassis and carrying at least a head substantially at a center of the head base; a pair of pinch rollers for forward play and reverse play arranged in a substantially symmetric design at opposite sides of the head; spring means for biasing the head base toward a stand-by position remote from a tape running plane defined by and between the capstans; a pair of engagement members engageable with the head base at a point offset from a center line of the chassis; and rotation transmission means for moving one of the engagement members, selected depending upon the direction of rotation of the motor, while in engagement with the head base at the offset point, thereby moving the head base from the stand-by position toward the tape running plane. The head base at the stand-by position is shifted toward the tape running plane, against the biasing force of the spring means, in one of oppositely oblique directions due to engagement with a selected one of the engagement members, so that one of the pinch rollers is pressed against a corresponding one of the capstans, while the other pinch roller remains uncontact with the other capstan.
In a preferable embodiment of the present invention, the chassis has a longitudinal groove along its center axis, into which a projection on the bottom of the head plate is received. In this embodiment, while the head base is moved from the stand-by position toward the tape running plane, the projection moves along the groove and acts as a pivot for slight rotation of the head base to guide the head base to be moved in the oblique direction.
In a modified embodiment, the chassis has a projection on its center axis, which is received in a longitudinal groove on the top surface of the head plate. Likewise, in this embodiment, while the head base is moved from the stand-by position toward the tape running plane, the projection moves along the groove and acts as a pivot for slight rotation of the head base to guide the head base to be moved in the oblique direction.
In each of the above-described embodiments, the projection preferably also act as a pivot for rotation of the head base at an extreme position in the longitudinal groove, which increases a contact pressure between the selected pinch roller and its corresponding capstan opposed thereto and, at the same time, separates the other pinch roller from its corresponding capstan.
In another embodiment of the present invention, the head base shift mechanism further comprises guide means for allowing slight rotation of the head base during movement from the stand-by position toward the tape running plane. The guide means comprises an upstanding member on the chassis and a guide groove formed at an upper end portion of the head base for receiving the upstanding member with a play in width. Specifically, the upstanding member engages a right-side edge of the guide groove while the head base moves in a right upward direction, whereas it engages a left-side edge of the guide groove while the head base moves in a left upward direction. Thus, an angle of oblique direction of movement of the head base is defined by engagement of the upstanding member and one of opposite edges of the guide groove. In a preferable application, the rotation transmission means still operates to move the head base after the selected pinch roller becomes contact with its corresponding capstan, so that the head base tends to rotate, substantially about a contact point between the selected pinch roller and the capstan, in a direction opposite to that during preceding movement from the stand-by position, thereby releasing the upstanding member from contact with the edge of the guide groove.
In still another embodiment of the present invention, the rotation transmission means comprises a switch arm driven by the motor to swing about a pivot on the center axis of the chassis, a pair of operating arms arranged symmetrically at opposite sides of the center axis of the chassis, each operating arm having a pivot base end and a leading end engageable with an end portion of the switch arm and including the engagement member. In this embodiment, when the switch arm swings in one direction, one of the operating arms rotates due to engagement between the leading end of the said operating arm and the end portion of the switch arm, which, in turn, moves the head base due to engagement with the engagement member of the said operating arm.
In another preferable embodiment, the head base shift mechanism of the present invention further comprises a lock means for retaining the head base in a lock position where one of the pinch rollers is in press-contact with its corresponding capstan. In this embodiment, each operating arm has a forked leading end with an inner projection and an outer projection of greater extension than the inner projection. The end portion of the switch arm engages with the outer projection while the head base is moved from the stand-by position toward the tape running plane. The end portion of the switch arm engages with the inner projection to unlock the head base from the lock position defined by the lock means.
In still another embodiment of the present invention, the chassis has a guide opening having a base end portion and a pair of oblique grooves extending from the base end portion in opposite oblique directions to separate from each other as they extend, a select boss movably received within the guide opening and a projection driven by the motor to move the select boss within the base end portion toward the lower end of one of the oblique grooves. This arrangement will specify one of the oblique directions during movement of the head base from the stand-by position. In this embodiment, the rotation transmission means preferably comprises a switch arm driven by the motor to swing about a pivot on the center axis of the chassis, a pair of operating arms arranged symmetrically at opposite sides of the center axis of the chassis, each operating arm having a pivot base end and a leading end engageable with a first end portion of the switch arm and including the engagement member. The projection that moves the select boss is formed as a second end portion of the switch arm opposite to the first end portion.